BS ISO 14705:2016 pdf download – Fine ceramics (advanced ceramics, advanced technical ceramics) — Test method for hardness of monolithic ceramics at room temperature
4.4 Apparatus
4.4.1 Testing machine, capable of applying a predetermined test force in the range of 4,903 N (0,5 kgf) to 98,07 N (10 kgf), preferably 9,807 N (1 kgf), in accordance with ISO 6507-2. Verification of the test force shall be carried out in accordance with ISO 6507-2. 4.4.2 Diamond indenter, in the shape of a right-angle pyramid with a square base, as specified in ISO 6507-1 and ISO 6507-2. Verification of the indenter shall be carried out in accordance with ISO 6507-2.
4.4.3 Measuring device, capable of measuring the indentation diagonals with a readout resolution of ±0,2 µm or finer. A numerical aperture (NA) between 0,60 and 0,95 for the objective lens for the microscope is recommended. Verification of the measuring device shall be carried out in accordance with ISO 6507-2.
NOTE Indirect verification can be carried out by means of standardized blocks calibrated in accordance with ISO 6507-3, following ISO 6507-2, or other approved and traceable ceramic standard reference blocks.
4.5 Test pieces
4.5.1 The test shall be carried out on a surface which is smooth, flat and free from foreign matter. The test piece shall be polished to permit accurate measurement of the diagonal lengths of the indentation. Preparation shall be carried out in such a way that any alteration of the surface hardness is minimized. Surfaces shall not be thermally or chemically etched. If applicable, residual surface stresses shall be removed by suitable polishing or annealing procedures.
4.5.2 The thickness of the test piece shall be at least 0,5 mm. It shall be at least 1,5 times the diagonal of the indentation, d, and at least 2 times the crack length, c, whichever is greater. No indentation damage shall be visible at the back of the test piece upon completion of the test.
4.6 Procedure
4.6.1 In general, the test shall be carried out at room temperature within the limits of 10 °C to 35 °C. Tests carried out under controlled conditions shall be made at a temperature of 23 °C ± 5 °C.
4.6.2 The test force shall be 9,807 N (1 kgf). In cases where significant chipping or lateral crack-spalling occurs or where the impression is too faint, the test forces within the range 4,903 N (0,5 kgf) to 196,1 N (20 kgf), listed in Table 2, may be used. Other instances where a heavier load may be required are where the grain structure is very coarse and the indentation area at lower loads may contact only a few grains of the material (e.g. a multiphase material).
4.6.3 The following items shall be confirmed before the test.
a) Check the zero of the measuring system.
b) Check the measuring system using a calibrated scale or certified indentation in a test block.
c) Check the operation of the loading system by performing a test on a certified test block.
d) Check the condition of the indenter by examining the indentation made in the test block. Replace the indenter, if necessary, by taking into account the conditions given in 4.6.10.
e) A test block with high hardness has to be used in order to obtain impressions in the same size range as expected during tests on ceramics.
4.6.4 The indenter shall be cleaned prior to and during the test series, as ceramic powders or fragments from the ceramic test piece can adhere to the diamond indenter.
4.6.5 The test piece shall be placed on a rigid support. The support surface shall be clean and free from foreign matter. It is important that the test piece lies firmly on the support, so that displacement cannot occur during the test.
4.6.6 Carefully adjust the illumination and focusing conditions, in order to obtain the optimum view and clarity of the indentation. Both indentation tips shall be in focus at the same time. Do not change the focus when measuring the distance from tip to tip.